1. Field of the Invention
The present invention relates generally to metallic laminates and more particularly to metallic laminates suitable for use in the electronics industry. Specifically, the present invention relates to an aluminum carrier-aluminum oxide layer with a layer of copper electrodeposited on the aluminum oxide layer and a barrier layer of brass electrodeposited on top of the layer of copper.
2. State of the Art
Copper foil finds utility in the production of printed circuit boards. It is desirable to protect the copper foil from the point of electroforming the copper foil to the point of laminating the copper foil to a polymeric substrate, as is typically done in the industry.
One method of protecting the copper foil involves electrodepositing the copper foil on top of an aluminum substrate. This aluminum substrate, or carrier as it is frequently termed, protects one side of the copper foil, typically termed the shiny side of the copper foil. The other side of the copper foil, i.e., the matte side, is adhered under elevated temperatures and pressures to a polymeric substrate. Subsequent to this procedure, the aluminum layer may be mechanically stripped away leaving an exposed pristine surface of copper. This surface of copper is masked and etched resulting in the desired circuitry in the form of a network of copper lines.
The aluminum carrier layer may be removed by chemical means as opposed to the aforementioned mechanical means. In this approach, the aluminum layer is chemically etched from the surface of the copper layer.
As aluminum readily oxidizes, the copper foil is actually electrodeposited on a layer of aluminum oxide. Difficulties may arise in employing aluminum as a carrier. For instance, copper atoms may diffuse into the aluminum carrier producing a laminate that is difficult to process, i.e., the interdiffusion of copper atoms into the aluminum layer results in a laminate which is not easily peelable. In the past, one technique utilized to overcome this problem has been to electrodeposit a thin layer of zinc on the matte side of the copper surface. This zinc layer minimizes the diffusion of copper atoms into the aluminum carrier layer. However, the use of a thin layer of zinc on the matte side of the copper foil does not alleviate the problem of the undercutting of the copper foil from the underlying polymeric substrate during etching. A thin layer of brass has not been utilized in the past because brass does not suppress the diffusion of copper atoms into the aluminum layer and, inter alia, creates release problems of the copper from the aluminum carrier.
The following U.S. patents describe inventions relating to copper foil laminates.
Lifshin et al., U.S. Pat. No. 4,431,710, describe a copper-clad laminate in which an initial copper film is formed on an aluminum carrier by vapor deposition at a temperature of between 100 degrees Celsius and 250 degrees Celsius.
Berdan et al., U.S. Pat. No. 3,969,199, describe an improved mechanically strippable copper plate on an aluminum carrier wherein the aluminum carrier is pretreated with an alkaline, aqueous, alkali metal zincate composition containing a small amount of one or more soluble cobalt or nickel salts and removing the zincate coating with acid prior to plating with copper.
Morisaki, U.S. Pat. No. 4,049,481, describes a method of electrodepositing a binary alloy consisting of zinc and tin on copper foil as a barrier layer to the migration of copper during heat press lamination onto an adhesive substrate.
Hutkin, U.S. Pat. No. 4,088,544, describes a method and a composite which relate to enhanced strippability of an aluminum carrier from the underlying copper foil and to improved adhesion between the copper foil and the underlying polymeric substrate.
Yates et al., U.S. Pat. No. 3,998,601, describe a copper foil laminate and a method of making a copper foil laminate wherein the laminate contains a release layer.
Grey, Jr. et al., U.S. Pat. No. 4,452,664, describe a method of making a copper-clad laminate wherein a copper film is vapor deposited on the matte side of an aluminum carrier.